CD24 negativity reprograms mitochondrial metabolism to PPARα and NF-κB-driven fatty acid β-oxidation in triple-negative breast cancer

CD24 is a well-characterized breast cancer (BC) stem cell (BCSC) marker. Primary breast tumor cells having CD24-negativity together with CD44-positivity is known to maintain high metastatic potential. However, the functional role of CD24 gene in triple-negative BC (TNBC), an aggressive subtype of BC, is not well understood. While the significance of CD24 in regulating immune pathways is well recognized in previous studies, the significance of CD24 low expression in onco-signaling and metabolic rewiring is largely unknown. Using CD24 knock-down and over-expression TNBC models, our in vitro and in vivo analysis suggest that CD24 is a tumor suppressor in metastatic TNBC. Comprehensive in silico gene expression analysis of breast tumors followed by lipidomic and metabolomic analyses of CD24-modulated cells revealed that CD24 negativity induces mitochondrial oxidative phosphorylation and reprograms TNBC metabolism toward the fatty acid beta-oxidation (FAO) pathway. CD24 silencing activates PPARα-mediated regulation of FAO in TNBC cells. Further analysis using reverse-phase protein array and its validation using CD24-modulated TNBC cells and xenograft models nominated CD24-NF-κB-CPT1A signaling pathway as the central regulatory mechanism of CD24-mediated FAO activity. Overall, our study proposes a novel role of CD24 in metabolic reprogramming that can open new avenues for the treatment strategies for patients with metastatic TNBC.

Metabolomic Rewiring Promotes Endocrine Therapy Resistance in Breast Cancer

Approximately one-third of endocrine-treated women with estrogen receptor alpha-positive (ER+) breast cancers are at risk of recurrence due to intrinsic or acquired resistance. Thus, it is vital to understand the mechanisms underlying endocrine therapy resistance in ER+ breast cancer to improve patient treatment. Mitochondrial fatty acid β-oxidation (FAO) has been shown to be a major metabolic pathway in triple-negative breast cancer (TNBC) that can activate Src signaling. Here, we found metabolic reprogramming that increases FAO in ER+ breast cancer as a mechanism of resistance to endocrine therapy. A metabolically relevant, integrated gene signature was derived from transcriptomic, metabolomic, and lipidomic analyses in TNBC cells following inhibition of the FAO rate-limiting enzyme carnitine palmitoyl transferase 1 (CPT1), and this TNBC-derived signature was significantly associated with endocrine resistance in patients with ER+ breast cancer. Molecular, genetic, and metabolomic experiments identified activation of AMPK-FAO-oxidative phosphorylation (OXPHOS) signaling in endocrine-resistant ER+ breast cancer. CPT1 knockdown or treatment with FAO inhibitors in vitro and in vivo significantly enhanced the response of ER+ breast cancer cells to endocrine therapy. Consistent with the previous findings in TNBC, endocrine therapy-induced FAO activated the Src pathway in ER+ breast cancer. Src inhibitors suppressed the growth of endocrine-resistant tumors, and the efficacy could be further enhanced by metabolic priming with CPT1 inhibition. Collectively, this study developed and applied a TNBC-derived signature to reveal that metabolic reprogramming to FAO activates the Src pathway to drive endocrine resistance in ER+ breast cancer.

SIGNIFICANCE

Increased fatty acid oxidation induced by endocrine therapy activates Src signaling to promote endocrine resistance in breast cancer, which can be overcome using clinically approved therapies targeting FAO and Src.

Vitamin B2 enables regulation of fasting glucose availability

Flavin adenine dinucleotide (FAD) interacts with flavoproteins to mediate oxidation-reduction reactions required for cellular energy demands. Not surprisingly, mutations that alter FAD binding to flavoproteins cause rare inborn errors of metabolism (IEMs) that disrupt liver function and render fasting intolerance, hepatic steatosis, and lipodystrophy. In our study, depleting FAD pools in mice with a vitamin B2-deficient diet (B2D) caused phenotypes associated with organic acidemias and other IEMs, including reduced body weight, hypoglycemia, and fatty liver disease. Integrated discovery approaches revealed B2D tempered fasting activation of target genes for the nuclear receptor PPARα, including those required for gluconeogenesis. We also found PPARα knockdown in the liver recapitulated B2D effects on glucose excursion and fatty liver disease in mice. Finally, treatment with the PPARα agonist fenofibrate activated the integrated stress response and refilled amino acid substrates to rescue fasting glucose availability and overcome B2D phenotypes. These findings identify metabolic responses to FAD availability and nominate strategies for the management of organic acidemias and other rare IEMs.

Abstract 3771: Mitochondrial metabolism and racial disparity of bladder cancer

Potential differences and mechanism in metabolism among bladder cancer (BLCA) patients of diverse race or ethnicities remain largely unexplored. Even though the incidence rate of BLCA in African Americans (AA) is nearly half as that of European Americans (EA), but AA have the worst survival. We performed the transcriptomics and metabolomics profiling in ancestry verified patients from AA and EA BLCA and observed mitochondrial complex activities were uniquely enriched in AA tumors compared to EA tumors. In addition, in vitro assay demonstrated differences in mitochondrial complex protein and activity between AA and EA BLCA. We further confirmed the reprogramming of mitochondrial metabolism using in vitro 13C labeled tracers in both AA and EA BLCA. Integration of metabolomics and transcriptomics data reveals the enrichment of mTOR pathway in AA BLCA. Our findings indicate that an elevated mitochondrial oxphos activity through mTOR activation could be a factor for AA BLCA progression and provide the rationale to examine mitochondrial specific inhibitors along with mTOR inhibitors to target BLCA on subset of patients from the AA community.

Citation Format: Karthik Reddy Kami Reddy, Jun Hyoung Park, Roni J. Bollag, Allison Bellman, Martha Terris, Seth P. Lerner, Leomar Y. Ballester, Yair Lotan, Benny Abraham Kaipparettu, Nagireddy Putluri. Mitochondrial metabolism and racial disparity of bladder cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 3771.

A mechanistic modeling framework reveals the key principles underlying tumor metabolism

While aerobic glycolysis, or the Warburg effect, has for a long time been considered a hallmark of tumor metabolism, recent studies have revealed a far more complex picture. Tumor cells exhibit widespread metabolic heterogeneity, not only in their presentation of the Warburg effect but also in the nutrients and the metabolic pathways they are dependent on. Moreover, tumor cells can switch between different metabolic phenotypes in response to environmental cues and therapeutic interventions. A framework to analyze the observed metabolic heterogeneity and plasticity is, however, lacking. Using a mechanistic model that includes the key metabolic pathways active in tumor cells, we show that the inhibition of phosphofructokinase by excess ATP in the cytoplasm can drive a preference for aerobic glycolysis in fast-proliferating tumor cells. The differing rates of ATP utilization by tumor cells can therefore drive heterogeneity with respect to the presentation of the Warburg effect. Building upon this idea, we couple the metabolic phenotype of tumor cells to their migratory phenotype, and show that our model predictions are in agreement with previous experiments. Next, we report that the reliance of proliferating cells on different anaplerotic pathways depends on the relative availability of glucose and glutamine, and can further drive metabolic heterogeneity. Finally, using treatment of melanoma cells with a BRAF inhibitor as an example, we show that our model can be used to predict the metabolic and gene expression changes in cancer cells in response to drug treatment. By making predictions that are far more generalizable and interpretable as compared to previous tumor metabolism modeling approaches, our framework identifies key principles that govern tumor cell metabolism, and the reported heterogeneity and plasticity. These principles could be key to targeting the metabolic vulnerabilities of cancer.

Patient-derived iPSCs link elevated mitochondrial respiratory complex I function to osteosarcoma in Rothmund-Thomson syndrome

Rothmund-Thomson syndrome (RTS) is an autosomal recessive genetic disorder characterized by poikiloderma, small stature, skeletal anomalies, sparse brows/lashes, cataracts, and predisposition to cancer. Type 2 RTS patients with biallelic RECQL4 pathogenic variants have multiple skeletal anomalies and a significantly increased incidence of osteosarcoma. Here, we generated RTS patient-derived induced pluripotent stem cells (iPSCs) to dissect the pathological signaling leading to RTS patient-associated osteosarcoma. RTS iPSC-derived osteoblasts showed defective osteogenic differentiation and gain of in vitro tumorigenic ability. Transcriptome analysis of RTS osteoblasts validated decreased bone morphogenesis while revealing aberrantly upregulated mitochondrial respiratory complex I gene expression. RTS osteoblast metabolic assays demonstrated elevated mitochondrial respiratory complex I function, increased oxidative phosphorylation (OXPHOS), and increased ATP production. Inhibition of mitochondrial respiratory complex I activity by IACS-010759 selectively suppressed cellular respiration and cell proliferation of RTS osteoblasts. Furthermore, systems analysis of IACS-010759-induced changes in RTS osteoblasts revealed that chemical inhibition of mitochondrial respiratory complex I impaired cell proliferation, induced senescence, and decreased MAPK signaling and cell cycle associated genes, but increased H19 and ribosomal protein genes. In summary, our study suggests that mitochondrial respiratory complex I is a potential therapeutic target for RTS-associated osteosarcoma and provides future insights for clinical treatment strategies.

Towards decoding the coupled decision-making of metabolism and epithelial-to-mesenchymal transition in cancer

Cancer cells have the plasticity to adjust their metabolic phenotypes for survival and metastasis. A developmental programme known as epithelial-to-mesenchymal transition (EMT) plays a critical role during metastasis, promoting the loss of polarity and cell-cell adhesion and the acquisition of motile, stem-cell characteristics. Cells undergoing EMT or the reverse mesenchymal-to-epithelial transition (MET) are often associated with metabolic changes, as the change in phenotype often correlates with a different balance of proliferation versus energy-intensive migration. Extensive crosstalk occurs between metabolism and EMT, but how this crosstalk leads to coordinated physiological changes is still uncertain. The elusive connection between metabolism and EMT compromises the efficacy of metabolic therapies targeting metastasis. In this review, we aim to clarify the causation between metabolism and EMT on the basis of experimental studies, and propose integrated theoretical-experimental efforts to better understand the coupled decision-making of metabolism and EMT.

Abstract P3-10-03: Exploiting p53-dependent functional duality of estrogen receptor-beta to repurpose tamoxifen for triple negative breast cancer therapy

Whether estrogen receptor beta (ERβ/ESR2) is a pro- or anti-oncogenic protein in breast cancer has been controversial. ERβ levels are generally high in triple-negative breast cancer (TNBC). Reports including the Cancer Genome Atlas (TCGA) show that about 80% of TNBC express mutant p53 and it is a major driver of these cancers. We tested the hypothesis that WT versus mutant status of p53 will have an important role in determining the duality of ERβ functions. We showed that ERβ directly binds to TP53 in human breast cancer cells. Using glutathione-S-transferase (GST)-pull down and co-imunoprecipitation assays, we have delineated the DNA binding domain (DBD) along with the hinge domain of ERβ and the C-terminal regulatory domain of p53 to be essential for the interaction. The highly sensitive in situ proximity ligation assay (PLA) showed that ERβ is capable of interacting with both wild type (WT) and mutant p53 in breast cancer cells and tumor tissues. ERβ and p53 antibodies validated for specificity were used for all experiments. Combination of proliferation, cell cycle, and apoptosis assays, RNAi technology, quantitative ChIP (qChIP), and real-time PCR (qRT-PCR) showed that ERβ is pro-proliferative in the context of WTp53, whereas it is anti-proliferative in the context of mutant p53 in multiple breast cancer cell lines. The p53-dependent diametrically opposite functions of ERβ were recapitulated in isogenic MDA-MB-231 TNBC cells (generated by CRISPR) that differ only in the presence of WT versus mutant p53. A major gain-of-function of mutant p53 is its ability to bind and inactivate tumor suppressor p73. We show that ERβ binds and sequesters mutant p53 from mutant p53−p73 complex leading to reactivation of p73. Consistent with these observations, immunohistochemistry (IHC) in TNBC patient tumor tissue microarray (TMA) showed that patients with tumors expressing mutant p53 along with high levels of ERβ were of smaller size and lower stage. Complementing these findings, our analysis of the subgroup of the basal-like/TNBC tumors expressing mutant p53 (but not WTp53) in the METABRIC dataset showed that patients with tumors expressing higher levels of ERβ RNA (ESR2) had significantly better breast cancer-specific survival. The finding that ERβ–mutant p53 combination prognosticates survival in TNBC is important as to date there are no effective prognostic markers for TNBC and suggest the potential for using ERβ−mutant p53 combination in stratification of TNBC into therapeutically actionable subgroups.Furthermore, our findings provide a mechanistic explanation for the functional duality of ERβ and the controversy over its pro-versus anti-tumorigenic role.Surprisingly, Tamoxifen (Tam) increased ERβ-mut-p53 interaction in TNBC cells leading to increased transcription of anti-proliferation genes and knockdown experiments showed that the effect on transcription was dependent on both p73 and ERβ. Importantly, when combined with doxorubicin (Adriamycin) Tam decreased several fold the IC50 of doxorubicin resulting in increased apoptosis. The combination was more effective in inhibiting TNBC xenograft tumor growth in vivo compared to either treatment alone. Significant clinical implications of these findings include the potential for treating patients with doxorubicin at much lower dose than what is currently used in the management of TNBC, thereby reducing its major cumulative dose side effects. Importantly, although at present Tam is not indicated for TNBC, our data suggest the possibility for repurposing Tam therapy alone or in combination with chemotherapy to treat TNBC stratified based on ERβ and p53 status. If validated in a clinical trial, our findings could lead to a therapy that is fundamentally better in terms of effectiveness, cost and time needed to reach the TNBC patients.

Citation Format: Gokul M Das, Utpal K Mukhopadhyay, Chetan C Oturkar, Christina Adams, Nadi Wickramasekera, Sanjay Bansal, Rajesh Medisetty, Austin Miller, Wendy M Swetzig, Laxmi Silwal-Pandit, Anne-Lise Borresen-Dale, Creighton J Creighton, Jun Hyoung Park, Santhi D Konduri, Alka Mukhopadhyay, Alexander Caradori, Benny Abraham Kaipparettu. Exploiting p53-dependent functional duality of estrogen receptor-beta to repurpose tamoxifen for triple negative breast cancer therapy [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr P3-10-03.

Abstract P3-06-12: Autophagy-mediated survival mechanism to c-Src inhibitor therapy in triple negative breast cancer

c-Src (Src) is a proto-oncogene involved in signaling that culminates in the control of multiple biological functions. Src is also one of the most frequently upregulated pathways in triple negative breast cancer (TNBC). Dysregulation of Src has been detected in TNBC and is strongly associated with tumor metastasis and poor prognosis. However, even after promising preclinical studies, Src inhibitors did not show major clinical advantage in unselected TNBC populations. We have previously published that metastatic TNBC has high energy-dependency to mitochondrial fatty acid beta-oxidation (FAO) and FAO activates Src by inducing autophosphorylation at Y419. However, our recent analysis suggests that as observed with the Src inhibitors, TNBC tumors treated with FAO inhibitors also develop drug-resistance and exhibit continuous tumor growth. Evaluation of their drug resistance mechanism revealed that while short-term inhibition of FAO or Src induces autophagic and apoptotic cell deaths, long-term inhibition results in autophagy-mediated drug resistance and survival. Further analyses suggest that FAO/Src inhibitors promote interferon regulatory factor 1 (IRF1) expression and activate mitogen-activated protein kinase kinase (MEK)/extracellular signal-regulated kinase (ERK) pathway via the induction of cellular reactive oxygen species (ROS) in TNBC. Activated MEK/ERK then suppresses IRF1 expression and induces survival pathways for drug resistance and tumor survival. Validation of in vitro findings using in vivo TNBC models confirmed that combination of FAO/Src inhibitors with MEK/ERK inhibitor or ROS scavenger provide significant benefit to overcome the therapeutic resistance of TNBC. These findings open-up new therapeutic opportunities to manage TNBC patients with currently non-targetable metastatic tumors.

Citation Format: Kwanghwa Jung, Junhyoung Park, Tirupataiah Sirupangi, Dongya Jia, Nishant Gandhi, Shivanand Pudakalakatti, Jessica Elswood, Weston Porter, Nagireddy Putluri, Xiang H.-F Zhang, Xi Chen, Pratip K. Bhattacharya, Chad J. Creighton, Michael T. Lewis, Jeffrey M. Rosen, Lee-Jun C. Wong, Gokul M. Das, C. Kent Osborne, Mothaffar F Rimawi, Benny Abraham Kaipparettu. Autophagy-mediated survival mechanism to c-Src inhibitor therapy in triple negative breast cancer [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr P3-06-12.

Therapeutic inhibition of mTORC2 rescues the behavioral and neurophysiological abnormalities associated with Pten-deficiency

Dysregulation of the mammalian target of rapamycin (mTOR) signaling, which is mediated by two structurally and functionally distinct complexes, mTORC1 and mTORC2, has been implicated in several neurological disorders1-3. Individuals carrying loss-of-function mutations in the phosphatase and tensin homolog (PTEN) gene, a negative regulator of mTOR signaling, are prone to developing macrocephaly, autism spectrum disorder (ASD), seizures and intellectual disability2,4,5. It is generally believed that the neurological symptoms associated with loss of PTEN and other mTORopathies (for example, mutations in the tuberous sclerosis genes TSC1 or TSC2) are due to hyperactivation of mTORC1-mediated protein synthesis1,2,4,6,7. Using molecular genetics, we unexpectedly found that genetic deletion of mTORC2 (but not mTORC1) activity prolonged lifespan, suppressed seizures, rescued ASD-like behaviors and long-term memory, and normalized metabolic changes in the brain of mice lacking Pten. In a more therapeutically oriented approach, we found that administration of an antisense oligonucleotide (ASO) targeting mTORC2's defining component Rictor specifically inhibits mTORC2 activity and reverses the behavioral and neurophysiological abnormalities in adolescent Pten-deficient mice. Collectively, our findings indicate that mTORC2 is the major driver underlying the neuropathophysiology associated with Pten-deficiency, and its therapeutic reduction could represent a promising and broadly effective translational therapy for neurological disorders where mTOR signaling is dysregulated.

Abstract 2448: Elucidating the metabolic plasticity of cancer by coupling gene regulation with metabolic pathways

Metabolic plasticity allows cancer cells to adjust their metabolic phenotypes to grow and metastasize in hostile environments. Both glycolysis and oxidative phosphorylation (OXPHOS) are adapted by cancer cells to meet their bioenergetic and biosynthetic requirements in a context-dependent manner. Despite the advance in studies focusing only on glycolysis or OXPHOS in cancer, it remains largely unknown how cancer cells orchestrate different metabolic phenotypes for better survival. To address this question, there is an urgent need to develop systemic approaches to quantitatively study the interplay between glycolysis and OXPHOS in cancer. Mathematical modeling approaches have been employed to elucidate cancer metabolic reprogramming. Constraint-based models including flux balance analysis based on conservation of mass have been the most widely used approaches to simulate cancer metabolism. In addition, modeling efforts have also been developed to identify anomalous gene activity involved in cancer metabolism. These computational studies offer a quantitative and dynamical perspective of cancer metabolism mostly focusing on either metabolic pathways or gene activities. However, the alteration of the metabolic activity is often coupled with the change in gene activity, and vice versa. Thus, to comprehensively characterize cancer metabolic reprogramming, a mathematical modeling framework integrating gene regulation with metabolic pathways is urgently needed. Here, we establish a theoretical framework to elucidate cancer metabolic plasticity through systems biology analysis of the coupling of gene regulation and metabolic pathways. Our modeling results demonstrate a direct association between the activities of AMPK and HIF-1, master regulators of OXPHOS and glycolysis respectively, with the activities of three metabolic pathways: glucose oxidation, glycolysis and fatty acid oxidation (FAO). Guided by the model, we develop metabolic pathway signatures to quantify the activities of glycolysis, FAO and the citric acid cycle of tumor samples by evaluating the expression levels of enzymes involved in corresponding processes. The association of AMPK/HIF-1 activity with metabolic pathway activity, predicted by the model and verified by analyzing the well-annotated metabolomic and transcriptomic data from a breast cancer patients’ cohort, is further validated by in vitro studies of aggressive triple negative breast cancer cell lines. We further investigate the existence of an aggressive hybrid metabolic phenotype that enables cancer cells metabolic plasticity for better survival and a metabolically inactive phenotype that may be employed by cancer cells under pressure. To the best of our knowledge, we are the first, or at least one of the first, to couple gene regulation with metabolic pathways to elucidate cancer metabolic plasticity.

Citation Format: Dongya Jia, Mingyang Lu, Kwang Hwa Jung, Jun Hyoung Park, José N. Onuchic, Benny Abraham Kaipparettu, Herbert Levine. Elucidating the metabolic plasticity of cancer by coupling gene regulation with metabolic pathways [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 2448.

TP53 Status as a Determinant of Pro- vs Anti-Tumorigenic Effects of Estrogen Receptor-Beta in Breast Cancer

BACKGROUND

Anti-tumorigenic vs pro-tumorigenic roles of estrogen receptor-beta (ESR2) in breast cancer remain unsettled. We investigated the potential of TP53 status to be a determinant of the bi-faceted role of ESR2 and associated therapeutic implications for triple negative breast cancer (TNBC).

METHODS

ESR2-TP53 interaction was analyzed with multiple assays including the in situ proximity ligation assay. Transcriptional effects on TP53-target genes and cell proliferation in response to knocking down or overexpressing ESR2 were determined. Patient survival according to ESR2 expression levels and TP53 mutation status was analyzed in the basal-like TNBC subgroup in the Molecular Taxonomy of Breast Cancer International Consortium (n = 308) and Roswell Park Comprehensive Cancer Center (n = 46) patient cohorts by univariate Cox regression and log-rank test. All statistical tests are two-sided.

RESULTS

ESR2 interaction with wild-type and mutant TP53 caused pro-proliferative and anti-proliferative effects, respectively. Depleting ESR2 in cells expressing wild-type TP53 resulted in increased expression of TP53-target genes CDKN1A (control group mean [SD] = 1 [0.13] vs ESR2 depletion group mean [SD] = 2.08 [0.24], P = .003) and BBC3 (control group mean [SD] = 1 [0.06] vs ESR2 depleted group mean [SD] = 1.92 [0.25], P = .003); however, expression of CDKN1A (control group mean [SD] = 1 [0.21] vs ESR2 depleted group mean [SD] = 0.56 [0.12], P = .02) and BBC3 (control group mean [SD] = 1 [0.03] vs ESR2 depleted group mean [SD] = 0.55 [0.09], P = .008) was decreased in cells expressing mutant TP53. Overexpressing ESR2 had opposite effects. Tamoxifen increased ESR2-mutant TP53 interaction, leading to reactivation of TP73 and apoptosis. High levels of ESR2 expression in mutant TP53-expressing basal-like tumors is associated with better prognosis (Molecular Taxonomy of Breast Cancer International Consortium cohort: log-rank P = .001; hazard ratio = 0.26, 95% confidence interval = 0.08 to 0.84, univariate Cox P = .02).

CONCLUSIONS

TP53 status is a determinant of the functional duality of ESR2. Our study suggests that ESR2-mutant TP53 combination prognosticates survival in TNBC revealing a novel strategy to stratify TNBC for therapeutic intervention potentially by repurposing tamoxifen.

Abstract P2-02-11: Combinational treatment of biguanides and fatty acid β-oxidation inhibitor in triple-negative breast cancers

Among breast cancers (BCs), the driver pathways and therapeutic targets are still poorly understood for triple negative (TN) BCs. Advances in cancer metabolism research over the last decade have enhanced our understanding on metabolic reprogramming in cancer therapy. We have previously shown that metabolic reprogramming to fatty acid β-oxidation (FAO) is a major energy pathway in metastatic TNBC. Moreover, we reported that FAO regulates c-Src, one of the frequently upregulated oncopathways in TNBC via autophosphorylation of Src at Y419. Since FAO inhibitors alone cannot effectively control the tumor progression in TNBC, suitable combination therapies with other metabolic targets are necessary. Recently increasing evidences show that anti-diabetic biguanides have attractive anticancer effect in various cancer types including BC. However, its significance as an anticancer drug is not well established due to parallel metabolic pathways that support tumor growth.

Phenformin, a biguanide derivative similar to metformin, has a greater potency than metformin. Like metformin, phenformin also inhibits mitochondrial electron transport chain (ETC) through complex I inhibition. In addition, biguanides lead to the activation of AMPK, which plays a key role in insulin signaling and energy sensing. Importantly, AMPK is an upstream regulator of FAO pathway because it can phosphorylate ACC to activate FAO. Considering the dependency of TNBC to FAO, we evaluated the therapeutic significance of the combination of biguanides(ETC inhibitors) and FAO inhibitors in TNBC progression and metastasis. We hypothesize that blocking both 'arms' of the pathway can provide more pronounced and durable responses in TNBCs. Our different in vitro and in vivo studies using TNBC cell line and PDX models suggest that the combination of both inhibitors can provide better therapeutic significance in metastatic TNBCs. This is a rationale and cost-effective metabolic approach to manage the currently non-targetable metastatic TNBCs. Further investigation into the clinical effectiveness of this combination may provide better treatment opportunities for TNBC patients.

Citation Format: Park JH, Jung KH, Vithayathil S, Jia D, Kaipparettu BA. Combinational treatment of biguanides and fatty acid β-oxidation inhibitor in triple-negative breast cancers [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P2-02-11.

Abstract P5-04-04: Withdrawn

This abstract was withdrawn by the authors.

Citation Format: Das GM, Kulkarni S, Oturkar C, Edge SB, Wilton JH, Wang J, Swetzig WM, Adjei AA, Bies R, Hutson AD, Morrison CD, Kaipparettu BA, Groman A, Kumar S, Capuccino H. Withdrawn [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P5-04-04.

Abstract P2-02-14: Metabolic regulation and drug resistance in c-Src activated triple negative breast cancer

c-Src (Src) is a proto-oncogene involved in signaling that culminates in the control of multiple biological functions. Src is also one of the most frequently upregulated pathways in triple negative breast cancer (TNBC). Dysregulation of Src has been detected in TNBC and is strongly associated with tumor metastasis and poor prognosis. However, even after promising preclinical studies, Src inhibitors did not show major clinical advantage in unselected TNBC populations. We have previously published that metastatic TNBC has high energy-dependency to mitochondrial fatty acid beta-oxidation (FAO) and FAO activates Src by inducing autophosphorylation at Y419. However, our recent analysis suggests that as observed with the Src inhibitors, TNBC tumors treated with FAO inhibitors also develop drug-resistance and continue tumor growth. Evaluation of their drug resistance mechanism revealed that while short-term inhibition of FAO or Src induces autophagic and apoptotic cell deaths, long-term inhibition results in autophagy-mediated drug resistance and survival. Further analyses suggest that FAO and Src inhibitors activate mitogen-activated protein (MAP) kinase kinase (MEK)/extracellular signal-regulated kinase (ERK) pathway via the induction of cellular reactive oxygen species (ROS) in TNBC. Activated MEK/ERK then induces survival pathways for drug resistance and tumor survival. Validation of in vitro findings using in vivo TNBC models confirmed that combination of FAO/Src inhibitors with MEK/ERK inhibitors can provide significant benefit to overcome the therapeutic resistance of TNBC. These findings open-up new therapeutic opportunities to manage TNBC patients with currently non-targetable metastatic tumors.

Citation Format: Jung KH, Park JH, Sirupangi T, Jia D, Gandhi N, Pudakalakatti S, Elswood J, Porter W, Putluri N, Zhang XH-F, Chen X, Bhattacharya PK, Creighton CJ, Lewis MT, Rosen JM, Wong L-JC, Das GM, Osborne CK, Rimawi MF, Kaipparettu BA. Metabolic regulation and drug resistance in c-Src activated triple negative breast cancer [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P2-02-14.

GLUT12 promotes prostate cancer cell growth and is regulated by androgens and CaMKK2 signaling

Despite altered metabolism being an accepted hallmark of cancer, it is still not completely understood which signaling pathways regulate these processes. Given the central role of androgen receptor (AR) signaling in prostate cancer, we hypothesized that AR could promote prostate cancer cell growth in part through increasing glucose uptake via the expression of distinct glucose transporters. Here, we determined that AR directly increased the expression of SLC2A12, the gene that encodes the glucose transporter GLUT12. In support of these findings, gene signatures of AR activity correlated with SLC2A12 expression in multiple clinical cohorts. Functionally, GLUT12 was required for maximal androgen-mediated glucose uptake and cell growth in LNCaP and VCaP cells. Knockdown of GLUT12 also decreased the growth of C4-2, 22Rv1 and AR-negative PC-3 cells. This latter observation corresponded with a significant reduction in glucose uptake, indicating that additional signaling mechanisms could augment GLUT12 function in an AR-independent manner. Interestingly, GLUT12 trafficking to the plasma membrane was modulated by calcium/calmodulin-dependent protein kinase kinase 2 (CaMKK2)-5'-AMP-activated protein kinase (AMPK) signaling, a pathway we previously demonstrated to be a downstream effector of AR. Inhibition of CaMKK2-AMPK signaling decreased GLUT12 translocation to the plasma membrane by inhibiting the phosphorylation of TBC1D4, a known regulator of glucose transport. Further, AR increased TBC1D4 expression. Correspondingly, expression of TBC1D4 correlated with AR activity in prostate cancer patient samples. Taken together, these data demonstrate that prostate cancer cells can increase the functional levels of GLUT12 through multiple mechanisms to promote glucose uptake and subsequent cell growth.

Pharmacological targeting of MYC-regulated IRE1/XBP1 pathway suppresses MYC-driven breast cancer

The unfolded protein response (UPR) is a cellular homeostatic mechanism that is activated in many human cancers and plays pivotal roles in tumor progression and therapy resistance. However, the molecular mechanisms for UPR activation and regulation in cancer cells remain elusive. Here, we show that oncogenic MYC regulates the inositol-requiring enzyme 1 (IRE1)/X-box binding protein 1 (XBP1) branch of the UPR in breast cancer via multiple mechanisms. We found that MYC directly controls IRE1 transcription by binding to its promoter and enhancer. Furthermore, MYC forms a transcriptional complex with XBP1, a target of IRE1, and enhances its transcriptional activity. Importantly, we demonstrate that XBP1 is a synthetic lethal partner of MYC. Silencing of XBP1 selectively blocked the growth of MYC-hyperactivated cells. Pharmacological inhibition of IRE1 RNase activity with small molecule inhibitor 8866 selectively restrained the MYC-overexpressing tumor growth in vivo in a cohort of preclinical patient-derived xenograft models and genetically engineered mouse models. Strikingly, 8866 substantially enhanced the efficacy of docetaxel chemotherapy, resulting in rapid regression of MYC-overexpressing tumors. Collectively, these data establish the synthetic lethal interaction of the IRE1/XBP1 pathway with MYC hyperactivation and provide a potential therapy for MYC-driven human breast cancers.

Abstract P6-06-04: Targeting replication stress in triple negative breast cancer treatment regimen: An emerging approach

Triple-negative breast cancers (TNBCs) represent aggressive heterogeneous subtype of breast cancer with poor clinical outcome. TNBCs have been reported to have high levels of replication stress due to i) various oncogene activations (C-myc or EGFR) ii) germline BRCA mutations iii) “BRCAness” in the absence of BRCA mutations in sporadic TNBCs. Replication stress is known to cause genomic instability, promote tumorigenesis and plays a critical role in therapy resistance in TNBCs. Therefore, targeting replication stress has emerged as an effective approach for better TNBC treatment through further downregulation of the remaining checkpoints to induce catastrophic failure of TNBC cells proliferation. Herein, we evaluated the anticancer efficacy of Carbazole Blue (CB), a synthetic analogue of Carbazole, on TNBC cells growth and progression. Our results demonstrated that CB inhibits short and long term viability of TNBC (MDA-MB-231, MDA-MB-468 and BT549) cells in a dose dependent manner without affecting normal mammary epithelial (MCF-10A) cells. In addition, CB treatment significantly reduced proliferation of TNBC cells, as evidenced by the BrdU proliferation assay. Consistent with this, our results further demonstrated that CB treatment induced G1/S cell cycle arrest and apoptosis in TNBCs. Importantly, systemic delivery of CB using nanoparticle-based delivery approach suppressed breast cancer growth without inducing toxicity, in preclinical orthotopic xenograft and PDX mouse models of TNBC. Furthermore, our gene microarray analysis revealed that CB treatment modulates the expression and activity of several genes known to be involved in DNA replication (CDC6, CDT1, MCMs, Claspin, POLE and PCNA) and associated DNA repair machinery such as (XRCC3, Exo1 and RAD51), which play pivotal roles in replication stress. Our results for the first time highlight the potential use of CB as a novel and potent therapeutic agent for treating TNBCs. As exploiting replication stress to treat cancer is gaining major interest, compound/s that may induce replication stress and inhibit DNA repair ability of cancer cells, has immense translational potential.

Citation Format: Rajamanickam S, Park JH, Bates K, Timilsina S, Eedunuri VK, Onyeagucha B, Subbarayalu P, Abdelfattah N, Jung KH, Favours E, Mohammad TA, Chen H-IH, Vadlamudi RK, Chen Y, Kaipparettu BA, Arbiser JL, Rao MK. Targeting replication stress in triple negative breast cancer treatment regimen: An emerging approach [abstract]. In: Proceedings of the 2017 San Antonio Breast Cancer Symposium; 2017 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2018;78(4 Suppl):Abstract nr P6-06-04.

Tobacco-Specific Carcinogens Induce Hypermethylation, DNA Adducts, and DNA Damage in Bladder Cancer

Smoking is a major risk factor for the development of bladder cancer; however, the functional consequences of the carcinogens in tobacco smoke and bladder cancer-associated metabolic alterations remain poorly defined. We assessed the metabolic profiles in bladder cancer smokers and non-smokers and identified the key alterations in their metabolism. LC/MS and bioinformatic analysis were performed to determine the metabolome associated with bladder cancer smokers and were further validated in cell line models. Smokers with bladder cancer were found to have elevated levels of methylated metabolites, polycyclic aromatic hydrocarbons, DNA adducts, and DNA damage. DNA methyltransferase 1 (DNMT1) expression was significantly higher in smokers than non-smokers with bladder cancer. An integromics approach, using multiple patient cohorts, revealed strong associations between smokers and high-grade bladder cancer. In vitro exposure to the tobacco smoke carcinogens, 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone and benzo[a]pyrene (BaP) led to increase in levels of methylated metabolites, DNA adducts, and extensive DNA damage in bladder cancer cells. Cotreatment of bladder cancer cells with these carcinogens and the methylation inhibitor 5-aza-2'-deoxycytidine rewired the methylated metabolites, DNA adducts, and DNA damage. These findings were confirmed through the isotopic-labeled metabolic flux analysis. Screens using smoke-associated metabolites and DNA adducts could provide robust biomarkers and improve individual risk prediction in bladder cancer smokers. Noninvasive predictive biomarkers that can stratify the risk of developing bladder cancer in smokers could aid in early detection and treatment. Cancer Prev Res; 10(10); 588-97. ©2017 AACR.

B-cell Receptor Signaling Regulates Metabolism in Chronic Lymphocytic Leukemia

Peripheral blood chronic lymphocytic leukemia (CLL) cells are quiescent but have active transcription and translation processes, suggesting that these lymphocytes are metabolically active. Based on this premise, the metabolic phenotype of CLL lymphocytes was investigated by evaluating the two intracellular ATP-generating pathways. Metabolic flux was assessed by measuring glycolysis as extracellular acidification rate (ECAR) and mitochondrial oxidative phosphorylation as oxygen consumption rate (OCR) and then correlated with prognostic factors. Further, the impact of B-cell receptor signaling (BCR) on metabolism was determined by genetic ablation and pharmacological inhibitors. Compared with proliferative B-cell lines, metabolic fluxes of oxygen and lactate were low in CLL cells. ECAR was consistently low, but OCR varied considerably in human patient samples (n = 45). Higher OCR was associated with poor prognostic factors such as ZAP 70 positivity, unmutated IGHV, high β2M levels, and higher Rai stage. Consistent with the association of ZAP 70 and IGHV unmutated status with active BCR signaling, genetic ablation of BCR mitigated OCR in malignant B cells. Similarly, knocking out PI3Kδ, a critical component of the BCR pathway, decreased OCR and ECAR. In concert, PI3K pathway inhibitors dramatically reduced OCR and ECAR. In harmony with a decline in metabolic activity, the ribonucleotide pools in CLL cells were reduced with duvelisib treatment. Collectively, these data demonstrate that CLL metabolism, especially OCR, is linked to prognostic factors and is curbed by BCR and PI3K pathway inhibition.Implications: This study identifies a relationship between oxidative phosphorylation in CLL and prognostic factors providing a rationale to therapeutically target these processes. Mol Cancer Res; 15(12); 1692-703. ©2017 AACR.

Abstract P6-01-07: Mitochondria-nuclear communication regulates epithelial-mesenchymal transition and metastasis in triple negative breast cancer

For triple negative breast cancer (TNBC), the driver pathways are still poorly understood. Advances in cancer metabolism research over the last decade have enhanced and modified our understanding on Warburg effect. It is now known that mitochondria in tumors are not always defective in their ability to carry out oxidative phosphorylation. Instead, in proliferating cells, mitochondrial energy pathways are reprogrammed to meet the challenges of macromolecular synthesis and to escape from apoptosis. Tumor initiating cells (TICs) maintain cancer stem cell properties and are known to play significant role in TNBC metastasis. Mitochondrial retrograde regulation (MRR) is a bidirectional communication between mitochondria and nucleus. MRR is triggered by mitochondrial functional demands and it responds in a continuous manner to change metabolic needs of the cell. Using transmitochondrial cybrid (cybrid) technology, we generated different cybrid models under common nuclear backgrounds of benign breast epithelium or TNBC. Mitochondria from cells with different cancer potential such as benign breast epithelium, moderately metastatic and highly metastatic breast cancer cell lines were studied under the common nuclear background to understand MRR-regulated TIC properties and cancer pathways. Using genomic, metabolomic, and proteomic approaches, we confirmed the significance of mitochondrial character in the regulation of epithelial mesenchymal transition (EMT), TIC and metastatic properties. Altogether, our results suggest that MRR is critical in TNBC TIC character and stemness.

Citation Format: Park JH, Jung KH, Sirupangi T, Vithayathil S, Jin F, Putluri V, Piyarathna DWB, Yotnda P, Bhat VB, Sreekumar A, Lewis MT, Coarfa C, Putluri N, Creighton CJ, Wong L-JC, Kaipparettu BA. Mitochondria-nuclear communication regulates epithelial-mesenchymal transition and metastasis in triple negative breast cancer [abstract]. In: Proceedings of the 2016 San Antonio Breast Cancer Symposium; 2016 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2017;77(4 Suppl):Abstract nr P6-01-07.

Modeling the Genetic Regulation of Cancer Metabolism: Interplay between Glycolysis and Oxidative Phosphorylation

Abnormal metabolism is a hallmark of cancer, yet its regulation remains poorly understood. Cancer cells were considered to utilize primarily glycolysis for ATP production, referred to as the Warburg effect. However, recent evidence suggests that oxidative phosphorylation (OXPHOS) plays a crucial role during cancer progression. Here we utilized a systems biology approach to decipher the regulatory principle of glycolysis and OXPHOS. Integrating information from literature, we constructed a regulatory network of genes and metabolites, from which we extracted a core circuit containing HIF-1, AMPK, and ROS. Our circuit analysis showed that while normal cells have an oxidative state and a glycolytic state, cancer cells can access a hybrid state with both metabolic modes coexisting. This was due to higher ROS production and/or oncogene activation, such as RAS, MYC, and c-SRC. Guided by the model, we developed two signatures consisting of AMPK and HIF-1 downstream genes, respectively, to quantify the activity of glycolysis and OXPHOS. By applying the AMPK and HIF-1 signatures to The Cancer Genome Atlas patient transcriptomics data of multiple cancer types and single-cell RNA-seq data of lung adenocarcinoma, we confirmed an anticorrelation between AMPK and HIF-1 activities and the association of metabolic states with oncogenes. We propose that the hybrid phenotype contributes to metabolic plasticity, allowing cancer cells to adapt to various microenvironments. Using model simulations, our theoretical framework of metabolism can serve as a platform to decode cancer metabolic plasticity and design cancer therapies targeting metabolism. Cancer Res; 77(7); 1564-74. ©2017 AACR.

Tunable luminescence from two dimensional BCNO nanophosphor for high-contrast cellular imaging

Multi-colour emitting nanophosphors provide a paradigm shift in rare-earth free biocompatible nanoprobes for in vitro and in vivo imaging applications.

Bifunctional Luminomagnetic Rare-Earth Nanorods for High-Contrast Bioimaging Nanoprobes

Nanoparticles exhibiting both magnetic and luminescent properties are need of the hour for many biological applications. A single compound exhibiting this combination of properties is uncommon. Herein, we report a strategy to synthesize a bifunctional luminomagnetic Gd2-xEuxO3 (x = 0.05 to 0.5) nanorod, with a diameter of ~20 nm and length in ~0.6 μm, using hydrothermal method. Gd2O3:Eu(3+) nanorods have been characterized by studying its structural, optical and magnetic properties. The advantage offered by photoluminescent imaging with Gd2O3:Eu(3+) nanorods is that this ultrafine nanorod material exhibits hypersensitive intense red emission (610 nm) with good brightness (quantum yield more than 90%), which is an essential parameter for high-contrast bioimaging, especially for overcoming auto fluorescent background. The utility of luminomagnetic nanorods for biological applications in high-contrast cell imaging capability and cell toxicity to image two human breast cancer cell lines T47D and MDA-MB-231 are also evaluated. Additionally, to understand the significance of shape of the nanostructure, the photoluminescence and paramagnetic characteristic of Gd2O3:Eu(3+) nanorods were compared with the spherical nanoparticles of Gd2O3:Eu(3+).

Eu3+ doped α-sodium gadolinium fluoride luminomagnetic nanophosphor as a bimodal nanoprobe for high-contrast in vitro bioimaging and external magnetic field tracking applications

Herein, we introduce a novel strategy for the synthesis of Eu3+ doped α-sodium gadolinium fluoride (α-NaGd0.88F4:Eu0.123+) based luminomagnetic nanophosphors using hydrothermal route. The synthesized nanophosphor has exceptional luminescent and paramagnetic properties in a single host lattice, which is highly desirable for biomedical applications. This highly luminescent nanophosphor with an average particle size ∼ 5±3 nm enables high-contrast fluorescent imaging with decreased light scattering. In vitro cellular uptake is shown by fluorescent microscopy that envisages the characteristic hypersensitive red emission of Eu3+ doped α-sodium gadolinium fluoride centered at 608 nm (5D0-7F2) upon 465 nm excitation wavelength. No apparent cytotoxicity is observed. Furthermore, time- resolved emission spectroscopy and SQUID magnetic measurements successfully demonstrate a photoluminescence decay time in microseconds and enhanced paramagnetic behavior respectively, which promises the applications of nanophosphors in biomedical studies. Hence, the obtained results strongly suggest that this nanophosphor could be potentially used as a bimodal nanoprobe for high-contrast in vitro bio-imaging of HeLa cells and external magnetic field tracking applications of luminomagnetic nanophosphors using permanent magnet.

Fatty Acid Oxidation-Driven Src Links Mitochondrial Energy Reprogramming and Oncogenic Properties in Triple-Negative Breast Cancer

Transmitochondrial cybrids and multiple OMICs approaches were used to understand mitochondrial reprogramming and mitochondria-regulated cancer pathways in triple-negative breast cancer (TNBC). Analysis of cybrids and established breast cancer (BC) cell lines showed that metastatic TNBC maintains high levels of ATP through fatty acid β oxidation (FAO) and activates Src oncoprotein through autophosphorylation at Y419. Manipulation of FAO including the knocking down of carnitine palmitoyltransferase-1A (CPT1) and 2 (CPT2), the rate-limiting proteins of FAO, and analysis of patient-derived xenograft models confirmed the role of mitochondrial FAO in Src activation and metastasis. Analysis of TCGA and other independent BC clinical data further reaffirmed the role of mitochondrial FAO and CPT genes in Src regulation and their significance in BC metastasis.

Abstract BS3-1: Dominance of mitochondria in determining the malignant phenotype

Mitochondria are semiautonomous organelles within cells that play an important role in cellular energy metabolism, free radical generation, and apoptosis. Mitochondria contain their own genome (mtDNA), which encodes a number of proteins critical for energy metabolism, particularly in oxidative phosphorylation. They are also the major source of generating reactive oxygen species (ROS) in the cell. Advances in cancer metabolism research over the last decade have enhanced and modified our understanding on Warburg effect. It is now known that mitochondria in tumors are not always defective in their ability to carry out oxidative phosphorylation. Instead, in proliferating cells, mitochondrial energy pathways are reprogrammed to meet the challenges of macromolecular synthesis and to escape from apoptosis. Mitochondrial retrograde regulation (MRR) is a bidirectional communication between mitochondria and nucleus. MRR is triggered by mitochondrial functional demands and it responds in a continuous manner to the changing metabolic needs of the cell. At present, it is not clear whether mitochondrial genomic status or metabolomic reprogramming affect nuclear genome stability. Also, limited evidence is available on the significance of proteins involved in the inter-genomic cross talk in the regulation of tumorigenesis. Transmitochondrial cybrids (cybrids) are a great utility for the study of the functional effects of mitochondria in a defined nuclear background. Cybrids are constructed by fusing enucleated cells harboring mitochondria of interest with ρ0 cells (mtDNA-depleted cells). Our approach of discovering mitochondria regulated pathways using cybrid models and their in vitro and in vivo validation in different breast cancer cell lines and patient derived xenograft models suggest that mitochondrial metabolic character and retrograde signaling are playing important roles in oncogenic transformation and metastasis. Importantly, mitochondria-nuclear crosstalk is critical in the regulation of some of the major cancer pathways. Compared to hormone regulated/responsive breast cancers, triple negative breast cancer patients suffer from worse overall survival, significantly shorter disease-free and post-recurrence survival. Due to the lack of known oncogenic drivers for triple negative breast cancer, clinical benefit from currently available targeted therapies is limited, and new therapeutic strategies are urgently needed. Thus, understanding MRR and mitochondria mediated oncogenic signature is critical in understanding the currently limited known etiology and treatment resistance of certain subgroups of cancers like the triple negative breast cancer.

Citation Format: Kaipparettu BA. Dominance of mitochondria in determining the malignant phenotype. [abstract]. In: Proceedings of the Thirty-Eighth Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2015 Dec 8-12; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(4 Suppl):Abstract nr BS3-1.

Abstract P1-07-06: Activation of oncogenic pathways by mitochondrial reprogramming in triple negative breast cancer

Triple negative breast cancer (TN BCa) Driver pathway is still poorly understood. Thus, it is important to identify the underlying mechanisms of triple negative breast cancer progression. Mitochondria, a semiautonomous organelle in cells, play an important role in cellular energy metabolism, free radical generation, and apoptosis. Mitochondria-nuclear crosstalk is a bidirectional pathway of communication between mitochondria and nucleus that influences many cellular and organismal activities. This crosstalk can regulate several oncogenic pathways involved in tumorigenesis. Using transmitochondrial cybrid (cybrid) technology, we generated different cybrid models under common nuclear background of TN BCa. Mitochondria from cells of different cancer potential including benign breast epithelium, moderately and highly metastatic breast cancer cell lines were used to understand cancer mitochondria regulated tumor pathways. Tumor and gene expression analysis suggested that among different cancer pathways, c-Src signaling pathway is one of the most consistently activated pathways in cybrids with TN BCa cancer mitochondria. Further analysis in parental cells and other tumor models suggested that autophosphorylation of c-Src is regulated by mitochondrial tumor characteristics. Our preliminary analysis also suggest that mitochondria targeted drugs are promising combination therapy for the management of Src-driven TN BCa. This finding is particularly important while considering the poor response rate observed after single drug therapy with Src family tyrosine kinase inhibitor Dasatinib in unselected TN BCa patients.

Citation Format: Jun Hyoung Park, Santhosh Kumar, Sajna Vithayathil, Kavisha Arora, Nagireddy Putluri, Efrosini Tsouko, Taraka R Donti, Daniel E Frigo, Chad J Creighton, Michael T Lewis, Arun Sreekumar, Lee-Jun Wong, Benny Abraham Kaipparettu. Activation of oncogenic pathways by mitochondrial reprogramming in triple negative breast cancer [abstract]. In: Proceedings of the Thirty-Seventh Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2014 Dec 9-13; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2015;75(9 Suppl):Abstract nr P1-07-06.

Probing highly luminescent europium-doped lanthanum orthophosphate nanorods for strategic applications

Herein we have established a strategy for the synthesis of highly luminescent and biocompatible europium-doped lanthanum orthophosphate (La0.85PO4Eu0.15(3+)) nanorods. The structure and morphogenesis of these nanorods have been probed by XRD, SEM, and TEM/HRTEM techniques. The XRD result confirms that the as-synthesized nanorods form in a monazite phase with a monoclinic crystal structure. Furthermore, the surface morphology shows that the synthesized nanorods have an average diameter of ∼90 nm and length of ∼2 μm. The HRTEM images show clear lattice fringes that support the presence of better crystal quality and enhanced photoluminescence hypersensitive red emission at 610 nm ((5)D0-(7)F2) upon 394 nm wavelength excitation. Furthermore, time-resolved spectroscopy and an MTT assay of these luminescent nanorods demonstrate a photoluminescent decay time of milliseconds with nontoxic behavior. Hence, these obtained results suggest that the as-synthesized luminescent nanorods could be potentially used in invisible security ink and high-contrast bioimaging applications.

Abstract P5-03-07: CD24 epigenetic regulation in breast cancer tissues and tumor initiating cells: Promoter specific analysis using next generation sequencing

CD24 negativity together with a positive expression of CD44 is considered as a marker for breast tumor initiating cells (breast cancer stem cells). We have previously reported that estrogen dynamically down regulate CD24 expression through an estrogen response element (ERE) present in the CD24 distal promoter. Further analysis of clinical breast cancer tissues suggested a frequent loss of CD24 expression in invasive breast cancers compared to the adjacent carcinoma in situ. Also, treatment with 5-AzaC could reverse the CD24 expression in many CD24 negative breast cancer cell lines. In order to understand the epigenetic regulation of CD24 expression and its correlation to hormonal status, the proximal promoter hypermethylation of CD24 gene was analyzed by Next Generation Sequencing (NGS) in DNA from clinical samples and established cell lines from breast cancer patients. DNA from blood, non-cancerous, and cancerous tissues from 73 breast cancer patients were used. There were approximately equal number of estrogen receptor alpha (ERa) positive and negative patients. DNA was also obtained from CD44+/CD24- and CD44+/CD24+ subpopulation FACS sorted from MCF7, SUM159 and MDA-MB231 breast cancer cell lines. CD24 proximal promoter region was PCR amplified from bisulfite converted DNA and prevalence of individual CpG methylation was quantified by NGS. The methylation pattern of individual CpGs suggested that CpGs close to the CD24 transcription start site was more methylated compared to the distant CpGs. Promoter methylation was significantly higher in breast cancer tissues compared to blood DNA. Analysis of clinical parameters showed a significantly higher methylation in ERα positive tumors compared to the negative tumors suggesting a hormonal regulation in CD24 epigenetic silencing. Analysis of ONCOMINE data confirmed this lower CD24 expression in ERα positive tumors. Importantly, analysis of sorted subpopulation from established breast cancer cell lines suggested that the CD24 epigenetic silencing is the major regulatory mechanism in maintaining low CD44+/CD24- subpopulation in cancer cell lines. Interestingly, though MCF7 cell lines have high CD24 expression with mostly unmethylated CD24 promoter, it contain less than 1% CD44+/CD24- subpopulation with stem cell like phenotype. NGS analysis discovered hypermethylation (>90%) of CD24 proximal promoter in that stem cell like subpopulation. Functional studies like mammosphere formation assay suggested that stem cell properties are higher in subpopulation with CD24 proximal promoter hypermethylation. Altogether, our results suggest that CD24 proximal promoter methylation maybe a hormonally regulated mechanism and epigenetic regulation of CD24 is important in maintaining the phenotype of the low prevalent breast tumor initiating population. Current studies are in progress to further understand the clinical and therapeutic significance of this regulation.

Citation Information: Cancer Res 2013;73(24 Suppl): Abstract nr P5-03-07.

Highly luminescent-paramagnetic nanophosphor probes for in vitro high-contrast imaging of human breast cancer cells

Highly luminescent-paramagnetic nanophosphors have a seminal role in biotechnology and biomedical research due to their potential applications in biolabeling, bioimaging, and drug delivery. Herein, the synthesis of high-quality, ultrafine, europium-doped yttrium oxide nanophosphors (Y(1.9)O(3):Eu(0.1)(3+)) using a modified sol-gel technique is reported and in vitro fluorescence imaging studies are demonstrated in human breast cancer cells. These highly luminescent nanophosphors with an average particle size of ≈6 nm provide high-contrast optical imaging and decreased light scattering. In vitro cellular uptake is shown by fluorescence microscopy, which visualizes the characteristic intense hypersensitive red emission of Eu(3+) peaking at 610 nm ((5)D(0)-(7)F(2)) upon 246 nm UV light excitation. No apparent cytotoxicity is observed. Subsequently, time-resolved emission spectroscopy and SQUID magnetometry measurements demonstrate a photoluminescence decay time in milliseconds and paramagnetic behavior, which assure applications of the nanophosphors in biomedical studies.

Graphene quantum dots derived from carbon fibers

Graphene quantum dots (GQDs), which are edge-bound nanometer-size graphene pieces, have fascinating optical and electronic properties. These have been synthesized either by nanolithography or from starting materials such as graphene oxide (GO) by the chemical breakdown of their extended planar structure, both of which are multistep tedious processes. Here, we report that during the acid treatment and chemical exfoliation of traditional pitch-based carbon fibers, that are both cheap and commercially available, the stacked graphitic submicrometer domains of the fibers are easily broken down, leading to the creation of GQDs with different size distribution in scalable amounts. The as-produced GQDs, in the size range of 1-4 nm, show two-dimensional morphology, most of which present zigzag edge structure, and are 1-3 atomic layers thick. The photoluminescence of the GQDs can be tailored through varying the size of the GQDs by changing process parameters. Due to the luminescence stability, nanosecond lifetime, biocompatibility, low toxicity, and high water solubility, these GQDs are demonstrated to be excellent probes for high contrast bioimaging and biosensing applications.

Transmitochondrial cybrids: tools for functional studies of mutant mitochondria

Mitochondrial functions are controlled by both mitochondrial DNA (mtDNA) and nuclear DNA. Hence, it is difficult to identify whether mitochondrial or nuclear genome is responsible for a particular mitochondrial defect. Cybrid is a useful tool to overcome this difficulty, where we can compare mitochondria from different sources in a defined nuclear background. Cybrids are constructed by fusing enucleated cells harboring wild type or altered mtDNA of interest with ρ(0) cells (cells lacking mtDNA) in which the endogenous mtDNA has been depleted. Therefore, cybrids are very useful in studying consequences of mtDNA alterations or other mitochondrial defects at the cellular level by excluding the influence of nuclear DNA mutations.

Mechanisms of estrogen receptor antagonism toward p53 and its implications in breast cancer therapeutic response and stem cell regulation

Estrogen receptor alpha (ERalpha) plays an important role in the onset and progression of breast cancer, whereas p53 functions as a major tumor suppressor. We previously reported that ERalpha binds to p53, resulting in inhibition of transcriptional regulation by p53. Here, we report on the molecular mechanisms by which ERalpha suppresses p53's transactivation function. Sequential ChIP assays demonstrated that ERalpha represses p53-mediated transcriptional activation in human breast cancer cells by recruiting nuclear receptor corepressors (NCoR and SMRT) and histone deacetylase 1 (HDAC1). RNAi-mediated down-regulation of NCoR resulted in increased endogenous expression of the cyclin-dependent kinase (CDK)-inhibitor p21(Waf1/Cip1) (CDKN1A) gene, a prototypic transcriptional target of p53. While 17beta-estradiol (E2) enhanced ERalpha binding to p53 and inhibited p21 transcription, antiestrogens decreased ERalpha recruitment and induced transcription. The effects of estrogen and antiestrogens on p21 transcription were diametrically opposite to their known effects on the conventional ERE-containing ERalpha target gene, pS2/TFF1. These results suggest that ERalpha uses dual strategies to promote abnormal cellular proliferation: enhancing the transcription of ERE-containing proproliferative genes and repressing the transcription of p53-responsive antiproliferative genes. Importantly, ERalpha binds to p53 and inhibits transcriptional activation by p53 in stem/progenitor cell-containing murine mammospheres, suggesting a potential role for the ER-p53 interaction in mammary tissue homeostasis and cancer formation. Furthermore, retrospective studies analyzing response to tamoxifen therapy in a subset of patients with ER-positive breast cancer expressing either wild-type or mutant p53 suggest that the presence of wild-type p53 is an important determinant of positive therapeutic response.

Scaffold Attachment Factor B1 (SAFB1) heterozygosity does not influence Wnt-1 or DMBA-induced tumorigenesis

Background

Scaffold Attachment Factor B1 (SAFB1) is a multifunctional protein which has been implicated in breast cancer previously. We recently generated SAFB1 knockout mice (SAFB1^-/-), but pleiotropic phenotypes including high lethality, dwarfism associated with low IGF-I levels, and infertility and subfertility in male and female mice, respectively, do not allow for straightforward tumorigenesis studies in these mice. Therefore, we asked whether SAFB1 heterozygosity would influence tumor development and progression in MMTV-Wnt-1 oncomice or DMBA induced tumorigenicity, in a manner consistent with haploinsufficiency of the remaining allele.

Methods

We crossed female SAFB1^+/- (C57B6/129) mice with male MMTV-Wnt-1 (C57B6/SJL) mice to obtain SAFB1^+/+/Wnt-1, SAFB1^+/-/Wnt-1, and SAFB1^+/- mice. For the chemical induced tumorigenesis study we treated 8 weeks old SAFB1^+/- and SAFB^+/+ BALB/c mice with 1 mg DMBA once per week for 6 weeks. Animals were monitored for tumor incidence and tumor growth. Tumors were characterized by performing H&E, and by staining for markers of proliferation and apoptosis.

Results

We did not detect significant differences in tumor incidence and growth between SAFB1^+/+/Wnt-1 and SAFB1^+/-/Wnt-1 mice, and between DMBA-treated SAFB1^+/+ and SAFB1^+/-mice. Histological evaluation of tumors showed that SAFB1 heterozygosity did not lead to changes in proliferation or apoptosis. There were, however, significant differences in the distribution of tumor histologies with an increase in papillary and cribriform tumors, and a decrease in squamous tumors in the SAFB1^+/-/Wnt-1 compared to the SAFB1^+/+/Wnt-1 tumors. Of note, DMBA treatment resulted in shortened survival of SAFB1^+/- mice compared to their wildtype littermates, however this trend did not reach statistical significance.

Conclusion

Our data show that SAFB1 heterozygosity does not influence Wnt-1 or DMBA-induced mammary tumorigenesis.

Novel egg white based 3D cell culture system for breast cancer research

Abstract #4060

Introduction: Over the last few years, much attention has been paid to the development and utilization of three-dimensional (3D) cell culture to replace classical two-dimensional (2D) monolayer cell culture systems grown as a flat layer on plastic. Not completely surprisingly, there are tremendous differences between cells in 2D and 3D culture. However, currently available 3D cell culture media are expensive for regular use by the majority of research laboratories and thus large scale use of 3D cell culture system is presently cost prohibited. In our search for a reliable and economically viable replacement for the expensive commercial 3D media, we hypothesized that avian egg white could be a potential alternative.
 Methods: Egg white-based chamber slide: Separated egg white from the chicken eggs and coated each wells of an eight well culture chamber with 80μl of egg white by careful heating at 600C on a heating block. After 30-60 minutes, the egg white becomes a semi-solid that adheres to the bottom of the well. The unstuck egg white is washed out by adding 500µl of growth medium and removing it slowly using a Pasteur pipette.
 Cell culture and analysis: To each well 2x103 immortalized human breast epithelial cells (MCF10A), were added in 0.5ml of appropriate culture medium. We have analyzed the growth curve of the acini, lumen formation, apoptosis and cell proliferation at different days post-culture. Apico/basal polarization of the acini was analyzed using appropriate antibodies. We have also cultured IGFR1-transformed MCF10A cells, different established human cell lines (MCF7, HEK293, HeLa, LNCaP, and Saos-2), and MMTV-PyMT transformed mouse mammary epithelial cells in their appropriate growth media. For comparative studies, we used a well-established reconstituted basement membrane matrix preparation (BM).
 Results: Our analysis shows that this simple avian egg white based system supports growth of cells in 3D, with significantly decreased cost. Specifically, the growth of MCF10A in egg white-based medium results in formation of acini with hollow lumens, apoptotic clearance of the cells in the lumen, and apico/basal polarization comparable to what has been described using established 3D culture media. There was no significant difference in MCF10A proliferation and acini size between egg white and BM. We have also observed similar morphology for different established cell lines, oncogene-transformed MCF10A, and mouse mammary epithelial cells between egg white and BM.
 Conclusion: Our data convincingly argue that egg white can be used as a suitable alternative model for 3D cell culture studies. We strongly believe that this simple and inexpensive method should allow researchers to perform 3D cell culture on a regular basis, and thus result in a dramatic increase of utilization of the 3D cell culture in research.

Citation Information: Cancer Res 2009;69(2 Suppl):Abstract nr 4060.

Estrogen-mediated downregulation of CD24 in breast cancer cells

We have previously reported on the relevance of the prevalence of CD44(+)/CD24(-/low) cells in primary breast tumors. To study regulation of CD24, we queried a number of publicly available expression array studies in breast cancer cells and found that CD24 was downregulated upon estrogen treatment. We confirmed this estrogen-mediated repression of CD24 mRNA by quantitative real-time PCR in MCF7, T47D and ZR75-1 cells. Repression was also seen at the protein level as measured by flow cytometry. CD24 was not downregulated in the ER alpha negative MDA-MB-231 cells suggesting that ER alpha was necessary. This was further confirmed by ER alpha silencing in MCF7 cells resulting in increased CD24 levels and by reintroduction of ER alpha into C4-12 cells resulting in decreased CD24 levels. Estrogen treatment did not alter half-life of CD24 mRNA and new protein synthesis was not essential for repression, suggesting a primary transcriptional effect. Histone deacetylase inhibition by Trichostatin A completely abolished the repression, but decrease of the ER alpha corepressors NCoR, LCoR, RIP140, silencing mediator of retinoid and thyroid hormone receptors, SAFB1 and SAFB2 by siRNA or overexpression of SAFB2, NCoR and silencing mediator of retinoid and thyroid hormone receptors had no effect. In silico promoter analyses led to the identification of two estrogen responsive elements in the CD24 promoter, one of which was able to bind ER alpha as shown by electrophoretic mobility shift assay and chromatin immunoprecipitation assay. Together, our results show that CD24 is repressed by estrogen and that this repression is a direct transcriptional effect depending on ER alpha and histone deacetylases.

[Experience in the management of children with diabetes mellitus]

Aerobic glycolysis, also referred to as the Warburg effect, has been regarded as the dominant metabolic phenotype in cancer cells for a long time. More recently, it has been shown that mitochondria in most tumors are not defective in their ability to carry out oxidative phosphorylation (OXPHOS). Instead, in highly aggressive cancer cells, mitochondrial energy pathways are reprogrammed to meet the challenges of high energy demand, better utilization of available fuels and macromolecular synthesis for rapid cell division and migration. Mitochondrial energy reprogramming is also involved in the regulation of oncogenic pathways via mitochondria-to-nucleus retrograde signaling and post-translational modification of oncoproteins. In addition, neoplastic mitochondria can engage in crosstalk with the tumor microenvironment. For example, signals from cancer-associated fibroblasts can drive tumor mitochondria to utilize OXPHOS, a process known as the reverse Warburg effect. Emerging evidence shows that cancer cells can acquire a hybrid glycolysis/OXPHOS phenotype in which both glycolysis and OXPHOS can be utilized for energy production and biomass synthesis. The hybrid glycolysis/OXPHOS phenotype facilitates metabolic plasticity of cancer cells and may be specifically associated with metastasis and therapy-resistance. Moreover, cancer cells can switch their metabolism phenotypes in response to external stimuli for better survival. Taking into account the metabolic heterogeneity and plasticity of cancer cells, therapies targeting cancer metabolic dependency in principle can be made more effective.